This invention relates to an operating handle locking device for preventing the operation of an operating handle of an electric switchgear such as a circuit interrupter.
An operating handle locking device of the conventional design is arranged as illustrated in FIGS. 1 to 3 in which the operating handle locking device is shown as being applied to a circuit interrupter. FIG. 1 is a side view of a circuit interrupter partly cut away, FIG. 2 is a perspective view of the circuit interrupter shown in FIG. 1, and FIG. 3 is an exploded perspective view of an operating handle and a handle cap of the conventional locking device. In FIGS. 1 to 3, a cover or a second housing 2 made of a molded electrically insulating material is mounted on a base or a first housing 1 made of a molded electrically insulating material. The cover has an aperture 2a and an inner wall 2b of the aperture 2a. An operating handle 3 made of a molded electrically insulating material and having a lever portion 3a extends through the aperture 2a of the cover 2 so that the operating handle 3 can be operated from the exterior of the circuit interrupter. The lever portion 3a of the operating handle 3 also has formed therethrough a through hole 3b. The operating handle 3 is placed on a handle arm 4 of an unillustrated operating mechanism of the circuit interrupter for the movement therewith, and a handle cap 5 made of a bent metallic sheet material is placed over the operating handle 3. One end of the handle cap 5 is formed into a substantially U-shaped engaging portion 5a for engaging the lever portion 3a of the operating handle 3 and having a pair of through holes 5b in the parallel portions of the engaging portion 5a. The other end of the handle cap 5 is formed into a substantially L-shaped blocking portion 5c. A locking member 6 such as a padlock is inserted through the through hole 3b of the operating handle 3 and the through holes 5b of the handle cap 5 and locks the handle cap 5 in engagement with the operating handle 3 so that it can not be disengaged therefrom. A trip button 7 for mechanically tripping the circuit interrupter from the exterior is provided for testing whether the alarm switch properly operates upon tripping, and whether the operating handle 3 can properly move from the trip position to the reset position when an externally operating lever (not shown) for externally operating the operating handle 3 is mounted on the front face of the circuit interrupter.
When the operating handle 3 is moved to the ON position (to the right) in FIG. 1 before placing the handle cap 5 onto the operating handle 3, the handle arm 4 is accordingly moved to move a pair of electrical contacts (not shown) of the circuit interrupter to the ON position through an operating mechanism (not shown). When the operating handle 3 is moved to the OFF position (to the left) in FIG. 1, the handle arm 4 is accordingly moved to move the pair of electrical contacts (not shown) to the OFF position through the operating mechanism (not shown).
However, there are circumstances in which such ON and OFF operations of the operating handle 3 should be prevented. For example, when electrical work such as inspection, repair and maintenance is to be done on the load side, the circuit interrupter should be held in the OFF position in order to protect the personnel doing the work against electrical shocks or the like. Alternately, the circuit interrupter should be held in the ON position where an electronic computer is in use which usually requires a continuing power supply. In such cases, in accordance with the ON or OFF position in which the operating handle 3 is to be held, the handle cap 5 is placed on the operating handle 3 with its engaging portion placed on either the left or right in FIG. 1. Then, the locking member 6 is inserted into the through hole 3b of the operating handle 3 and the through hole 5b of the handle cap 5 which are aligned with each other to lock the handle 3 and the handle cap 5.
FIGS. 1 and 2 illustrate the circuit interrupter held in the OFF position. In this state, the operation of the operating handle 3 is prevented by the blocking portion 5c of the handle cap 5 which abuts against the inner wall 2b of the cover 2. Since the operating handle 3 cannot be moved to the ON position (to the right in the figure) in the state shown in FIGS. 1 and 2, the electrical contact of the circuit interrupter cannot be closed. When the operating handle 3 is similarly locked as described above with the operating handle 3 held in the ON position (right in the figure), the electrical contact is prevented from moving into the OFF position.
However, conventional operating handle locking devices for electrical switchgear such as a circuit interrupter have been constructed according to special specifications since customer orders are few and far between, so that a standard type circuit interrupter must usually be specially rebuilt to accomodate an operating handle locking device. More specifically, the rebuilding has usually been achieved by removing the cover 2 from the base 1 and disengaging the operating handle 3 from the handle arm 4, and then forming the through hole 3b in the lever portion 3a of the operating handle 3. Such rebuilding is therefore, time-consuming and makes the circuit interrupter more expensive, and this also allows dust and foreign matter to enter the circuit interrupter when the cover 2 is removed from the base 1, decreasing reliability. If the through hole 3b is formed in each operating handle of a standard circuit interrupter in the factory in order to solve the above problem, the molding die and the molding operation become complicated, and the cost of a standard circuit interrupter which does not use an operating handle locking device becoming increased. Further, if the trip button is erroneously depressed at the time of locking the operating handle in the ON position, the internal mechanism is brought into the tripped state, so that the meaning of locking the interrupter in the ON position is lost.